Circular seal for NXT cable opening - part sourcing

[Sdpaddler50]

Does anyone know where I can buy one of these black, rubber seals for the annular space at the bottom of a NXT dome radar? It seals the opening where the cables pass through. Thanks.

 

[colemj]

Looks like a plain rubber grommet. https://www.mcmaster.com/rubber-grommets/grommets-6/